2005 Yukon Denali XL Need to replace the seals at the rear evaporator connection, under the vehicle, but cannot get the connections free. Nuts came off fine and I've tried heat and penetrant, but the connection aluminum blocks are seized on their studs. Asked a great independent shop, he said nobody can get them off. Had a local automotive radiator and A/C shop try but they gave up too. I have a set of new lines on the way (I'll eventually need them anyway I'm sure), but is there any trick I should try first to get these off intact?